1. Field of the Invention
The present invention relates to a lifting column for treatment tables, hospital- and care beds.
2. The Prior Art
Hospital beds comprise a lower frame equipped with drive wheels and an upper frame connected to a support for a mattress. The upper frame can as a whole be raised and lowered to assume a desired height above floor level, just as it can be tilted over a transverse axis (Trendelenburg position). Raising and lowering of the upper frame may be obtained in various ways, for instance in that the upper frame is connected to the lower frame with a scissor mechanism driven by a linear actuator, as for instance mentioned in EP 498 111 B2 J. Nesbit Evans & Co. Ltd. Another way is by equipping the bed with four telescopic legs, cf. DE 298 00 015 U1 Joh. Stiegelmeyer GmbH & Co. KG. More specifically, the invention departs from the type of bed, where the upper frame is carried by a single telescopic column at each end, and where the columns are secured to the lower frame in its longitudinal centre axis. This type of construction is for instance shown in EP 98 2 018 A2 Linet Spol SRO and DE 298 04 283 Dewert Antriebs- and Systemtechnik GmbH & Co. KG.
The strength and rigidity demands on these columns are rather large. Besides from influences from axial forces the lifting columns must be able to withstand significant torque loads, typically as a result thereof, that one or more people are sitting on the edge of the bed. Further, as a result of this, torque loads also appear on the columns in the longitudinal direction of the bed. A Trendelenburg-adjustment also causes torque loads as the upper frame is inclined, as well as it causes forces to occur on the column in the longitudinal direction of the bed. When the bed is transported by manually pushing/pulling the head and/or the foot board of the bed this also causes horizontal forces on the columns.
WO 01/74198 A1 Linak discloses a lifting column, able to withstand the different considerable forces and torques, which occur in such a bed structure. The lifting column comprises a surrounding telescopic casing having three members, in which a three-membered telescopic guide is contained at either sides, each having a lower member, intermediate member and outermost member. The two intermediate members and the two outermost members are interconnected by means of a yoke. The intermediate members are extended by means of a linear actuator located between the two guides and connected to a base plate and the yoke between the two intermediate members. For extending the outermost member, a chain drive is provided at each side, with a chain around two pulley wheels. One of the chain lengths is connected to the lower member, while the other length has a rod connected to the yoke for the two outermost members. The topmost chain wheels are interconnected and secured to the two intermediate members. This causes the outermost member to extend synchronously with the extension of the intermediate member. As it can be perceived, the structure is voluminous and complicated and as a consequence of this expensive to manufacture.
The object of the invention is to provide a simplification of such a column structure.